Timeslider breaks after 1000 revisions on HTML imported pads

[davue]

Tested on:

• Etherpad: 1.8.14
• Browsers: Chrome 94.0.4606.81 and Firefox 94.0.1
• Clients: Private instance and rich.etherpad.com
• Node: 12.18.0

Steps to reproduce:

1. Create a new pad and fill it with some content
2. Export the pad as HTML
3. Create a second pad and import the HTML from the first pad
4. Create enough changes to make more than 1000 revisions

What I expected to happen:
The timeslider would work normally

What actually happened:
Revisions after 1000 are working but all revisions < 1000 simply show the content of revision 1000.

Additional Information

• Also affects pads which were edited by the /setHTML API endpoint (which we internally use for applying templates)
• Most likely related to This .etherpad contents breaks timeslider playback #5214
• You can see the bug in action here (as long as the pad is kept alive): https://rich.etherpad.com/p/test3

[JohnMcLear]

https://github.com/ether/etherpad-lite/blob/develop/src/tests/frontend/specs/timeslider_revisions.js -- note that this only creates 100 revisions. Steps you can probably take to move things forward

• Extend timeslider_revisions.js to do a test with much more revisions (IE 1k+) and see if it fails in testing or not.

I would hazard a guess that the failure is due to the changeset loading method which probably needs to be rewritten as it's afaik code that hasn't been touched in several years.

TBH though I think we really need to think about the timeslider. I hate that it's a second rate citizen on it's own page and I'd strongly advocate moving the time-slider into the main pad editor and while we're at it expose more functionality for plugins such as the ability to replay the pad in real time... But these things are probably out of the scope of this bug.

[webzwo0i]

Could you test if applying #5253 fixes this problem?

[davue]

Nope, this sadly does not fix the issue @webzwo0i

[webzwo0i]

I tested it and for me it fixes the problem. Can you try and disable minify in the config (setting minify:false), go to a timeslider that has this bug, hit play and open the error console to see what exceptions are thrown?

The exception shown here is gone for me after applying #5253

insert@http://localhost:9001/javascripts/lib/ep_etherpad-lite/static/js/timeslider.js?callback=require.define&v=76afa96a:3680:21
(module ep_etherpad-lite/static/js/Changeset.js)/exports.mutateTextLines@http://localhost:9001/javascripts/lib/ep_etherpad-lite/static/js/timeslider.js?callback=require.define&v=76afa96a:3870:13
applyChangeset@http://localhost:9001/javascripts/lib/ep_etherpad-lite/static/js/timeslider.js?callback=require.define&v=76afa96a:5910:15
goToRevision@http://localhost:9001/javascripts/lib/ep_etherpad-lite/static/js/timeslider.js?callback=require.define&v=76afa96a:6002:36
update@http://localhost:9001/javascripts/lib/ep_etherpad-lite/static/js/timeslider.js?callback=require.define&v=76afa96a:6008:21

[davue]

Ok you're right, this partially fixed the problem. 👍

At least for imports and the setHTML endpoint. I was testing it using the copyPadWithoutHistory endpoint which still breaks the timeslider.

Steps to reproduce:

1. Copy an existing pad into a new one using copyPadWithoutHistory
2. Create over 1000 revisions in the new pad
3. Try to use the timeslider for revisions < 1000

Should I open up a new issue since this is not directly HTML related but specific to pad copying?

Edit:
This is the only error visible in the log when this happens:

[2021-11-17 14:12:44.288] [WARN] console - failed to compose cs in pad: g.tySn8Q2Aogt2SBWO$17835229-f8b2-4736-b137-36fdf82b04f7  startrev: 0  current rev: 2
[2021-11-17 14:12:44.288] [ERROR] console - Error while handling a changeset request for g.tySn8Q2Aogt2SBWO$17835229-f8b2-4736-b137-36fdf82b04f7 Error: Failed assertion: mismatched composition of two changesets { start: 0, granularity: 10, requestID: 11367 }

[davue]

It looks like that copyPad works without any issues. Only copyPadWithoutHistory seems to be affected by this bug.

Is there another way to clear the history of a pad to have a workaround?

[SamTV12345]

@Gared Is creating a fix for that so you can remove the history of a pad and its revisions

[SamTV12345]

Gared just checked locally with 25k versions. It seems like this could be caused by a corrupt pad which occurs when Etherpad crashes and hasn't finished writing to the database or the server crashes during a transaction. cc @Gared